Method for controlling dephlegmators



FROM

STRIPPER METHOD C. G. MITCHELL FOR CONTROLLING DEPHLEGMATORS Filed June 12, 1958 l 8 GASOLINE 36 I I I7 I P I l l 2|.

i i 27 26 24 E i I I [CONDENSED on.

T0 STRIPPER INVENTOR.

C.G. MITCHELL TORNEKS 2,974,100 IVIETHOD FOR CONTROLLING DEPHLEGMATORS Charles G. Mitchell, Odessa, Tex., assignor to'Phillips Petroleum Company, a corporation of Delaware Filed June 12,1958, Ser. No. 741,565

2 Claims. (Cl. 208-341) This invention relates to method and apparatus for con trolling dephlegmators.

In the operation of dephlegmators, which are used for condensing lean oil entrained in gasoline and steam vapors, it has been conventional practice to control the rate of addition of water reflux to the top of the dephlegmator to maintain a constanttemperature of the overhead vapors. It has also been conventional practice to use a liquid level controller for regulating the rate of flow of condensed oil from the'dephlegmator. An attempt was made to control the overheadvapor temperature so that all of the lean oil entrained in the gasoline vapors would be condensed with a minimum amount of gasoline vapors being condensed. Condensed gasoline vapors are of less value than lean oil. Therefore, it is advantageous to keep substantiallyall of the entrained lean oil frompassing overhead with the gasoline vapors, since the lean oil which is passed overhead with the gasoline vapors will be sold as natural gasoline and it will be necessary to add make-up lean oil which costs more than natural gasoline.

Another difliculty arises due to changes in the feed to the gasoline recovery system due to changes in feed supply. As is well known, the condensed hydrocarbon oil is recycled to the stripper or still for recovery of gasoline dissolved therein. At times, the gasoline contains a large quantity of heavier hydrocarbons which are condensed with the absorber oil. These heavier ends are then returned to the stripper which results in an excessive re cycle stream which, in turn, greatly reduces the capacity of the still. Therefore, it is desirable to prevent excessive buildup of the heavier components of the natural gasoline.

The following are objects of my invention.

An object of my invention is to provide apparatus for controlling dephlegmator operation. A further object is to provide improved method of dephlegmator operation. A further object of my invention is to provide a system for control designed to eliminate excessive loss of absorber oil and to eliminate excessive recycle of the heavier components of the gasoline.

Other objects and advantages of the invention will be apparent to one skilled in the art upon reading this disclosure. Accompanying and forming a part thereof is a drawing illustrating my invention.

The invention is broadly based upon the use of a ratio controller to regulate the return flow of reflux water into the top of the dephlegmator, the ratio controller operat-,

ing in response to changes in flow of condensed oil returned to the stripper and in response to the temperature of the overhead gasoline vapors. This system provides a system to give a substantially constant end point for the natural gasoline while preventing loss of oil and excessive liquid return to the stripper or still.

The invention can be best understood by reference to the drawing. In this drawing the vapors from a stripper (not shown) are passed to the dephlegmator by means of conduit 11. In this tower, the vapors pass up through the column for removal through conduit 12 while the o 609 mols of water per day to give a gasoline having an lean oil is condensed in the lower portion of the tower as a result of reflux liquid supplied by conduit 13, this; conduit removing condensed liquid from an intermediate Conduit 13 is provided with a 7 pump 16, heat exchanger 17, and motor valve. 18. Liquid tray 14 in the tower.

level controllers 19 and 21 are provided in the lower end portion of the dephlegmator, controller 19 being oper atively connected to valve 22 for water removal through conduit 23. Controller 21 is 'operatively connected to motor valve 24 in conduit 26, condensed oil being passed therethrough to the stripper.

A flow transmitter27 is attached toline 26' through which the condensed oil is returned to the stripper. The output from transmitter 27 is passed to ratio controller 28. A temperature transmitter 29 is connected to con-' duit 12. The output of temperature transmitter 29 is also connected to ratio. controller 28. The output from ratio controller 28 is connected to motor valve 18.

In operation, an attempt is made to maintain the rate of flow of condensed hydrocarbons substantially constant. If the rate of flow of condensed oil passing through line 26 increases, the signal from flow transmitter 27 is changed and ratio controller 28 decreases the rate of flow of reflux liquid into the top of tower 10. This results-in an increase in the temperature of the overhead vapors and reduces the rate of condensation in the dephlegmator- This increase in temperature of the overhead changes the signal which is sent from temperature transmitter 29 to' ratio controller 28 which, in turn, slightly increases the Conversely, a-

rate of reflux addition into the column. decrease in flow of condensed oil through conduit 26 will result in an increase in the rate of reflux supply which will be, in turn, adjusted as a result of the resulting change in overhead temperature. This series of operations results in the ratio controller 28 adjusting the amount of reflux to control both the temperature of the overhead vapors and the rate of flow of reflux liquid supplied to the dephlegmator so as to maintain a more nearly constant end point of the overhead vapors.

The recovery of natural gasoline from column 10 is obtained by cooling the vapors in condenser 31 and introducing them into chamber 32. Non-condensed material is passed to a flare through conduit 33, this conduit 7 being provided with back pressure regulator 34. Condensed gasoline is recovered by means of conduit 36.

The following example illustrates operation using my invention.

Example In one plant, the feed is supplied to the dephlegmator at 400 F. and a pressure of 260 p.s.i.g., this feed comprising 12 million standard cubic feet per day of hydrocarbons and 11,185 mols of water per day. Water and oil are condensed in the column, the water being removed from the bottom of the tower. The condensed oil is removed at 280 F. and returned to the stripper. The reflux liquid is removed at about 250 F. and cooled to a temperature in the range of to F. Ap-

proximately 9,000 gallons per hour of reflux are returned. The vapors are removed from the top of the tower at a temperature within the range of 140 to F., this range ticular operation provides an overhead of 11.6 million standard cubic feet per day of hydrocarbons containing API gravity of 51 at 100 F.

Obviously, additional control features can be incor- Patented Mar. 7, 1961 porated and the present drawing is submitted in simplified form in order to emphasize the improvements in operation according to my invention. Transmitter 27 is described on pages 14 and 15 of. Bulletin 98097 dated 1953 of the Taylor Instrument Companies of Rochester, New York. 7 of the same bulletin. Ratio controller 28 is described on page 4 of Bulletin 98158 dated August 1945 of the Taylor Instrument Companies.

As many possible embodiments can be made of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not as unduly limiting the invention.

I claim:

1. A method for recovery of gasoline vapors from a mixture containing the same and some absorber oil un-, avoidably entrained when said vapors have been stripped from a rich absorber oil obtained in the recovery of natural gasoline which comprises feeding the vapor mixture to a dephlegmation zone, condensing oil in said zone, removing gasoline vapor overhead from said zone, re-

Transmitter 29 is described on pages 6 and crease in the flow of condensed oil and decreasing the amount of water circulated in response to a decrease in the temperature of the overhead vapors, the net efiect of said changes being such that when the volume of condensed oil removed increases the flow rate of cooling water is adjusted to provide an increase in the temperature of the vapors removed overhead and vice versa.

2. A method for recovery of gasoline vapors from a mixture containing the same and some absorber oil unmoving condensed oil from the lower portion of said zone, recirculating water from an intermediate portion of said zone to the upper portion thereof to provide cool-' avoidably entrained when said vapors have been stripped from a rich absorber oil obtained in the recovery of natural gasoline which comprises feeding the vapor mixture to a dephlegmation zone, condensing oil in said zone, removing gasoline vapor overhead from said zone, removing condensed oil from the lower portion of said zone, recirculating water from an intermediate portion of said zone to the upper portion thereof to provide cooling of said upper portion, and adjusting the amount of water recirculated so that when the volume of condensed oil increases the cooling water flow rate is varied to provide an increase in the temperature of vapors removed overhead thereby decreasing the volume of condensed oil removed and vice versa.

References Cited in the tile of this patent UNITED STATES PATENTS 

1. A METHOD FOR RECOVERY OF GASOLINE VAPORS FROM A MIXTURE CONTAINING THE SAME AND SOME ABSORBER OIL UNAVOIDABLY ENTRAINED WHEN SAID VAPORS HAVE BEEN STRIPPED FROM A RICH ABOSRBER OIL OBTAINED IN THE RECOVERY OF NATURAL GASOLINE WHICH COMPRISES FEEDING THE VAPOR MIXTURE TO A DPHLEGMATION ZONE, CONDENSING OIL IN SAID ZONE, REMOVING GASOLINE VAPOR OVERHEAD FROM SAID ZONE, REVING CONDENSED OIL FROM THE LOWER PORTION OF SAID ZONE, RECIRCULATING WATER FEOM AN INTERMEDIATE PORTION OF SAID ZONE TO THE UPPER PORTION THEREOF TO PROVIDE COOLING OF SAID UPPER PORTION, DETERMINING CHANGES IN THE AMOUNT OF CONDENSED OIL REMOVED FROM THE LOWER PORTION OF SAID ZONE, DETERMINING CHANGES IN THE TEMPERATURE OF THE VAPOR REMOVED OVERHEAD FROM SAID ZONE, AND INCREASING THE AMOUNT OF WATER RECIRCULATED IN RESPONSE TO A DECREASE IN FLOW OF CONDENSED OIL, INCREASING THE AMOUNT OF WATER RECIRCULATED IN RESPONSE TO AN INCREASE IN THE TEMPERATURE OF THE OVERHEAD VAPORS, DECREASING THE AMOUNT OF WATER REECIRCULATED IN RESPONSE TO AN INCREASE IN THE FLOW OF CONDENSED OIL AND DECREASING THE AMOUNT OF WATER CIRCULATED IN RESPONSE TO A DECREASE IN THE TEMPRERATURE OF THE OVERHEAD VAPORS, THE NET EFFECT OF SAID CHANGES BEING SUCH THAT WHEN THE VOLUME OF CONDENSED OIL REMOVED INCREASED THE FLOW RATE OF COOLING WATER IS ADUJSTED TO PROVIDE AN INCREASE IN THE TEMPERATURE OF THE VAPORS REMOVED OVERHEAD AND VICE VERSA. 